Imaging camera parameters and description

Introduction

A detailed description of the imager can be found in Gunn et al. (1998) and in the project book. This page summarizes the most important information needed to understand the data it produces:

• imaging camera parameters
• filter curves
• arrangement of CCDs on the imaging camera
• CCD nonlinearity

Imaging camera parameters

Transmission curves

The photometric flux calibration web page is essential reading for those wishing to understand the SDSS photometric system. There is a long page describing transformations between SDSS (ugriz) and Kron-Cousins (UBVR_cI_c) photometry.

SDSS system response plot

The solid response curves show the througput defining the survey's photometric system, which includes extinction through an airmass of 1.3 at Apache Point Observatory. For reference, the dashed curves do not include any atmospheric extinction. These are sometimes loosely referred to as "filter curves" although they do include the full system response from atmosphere to detector.

Repeat photometry of most stars in stripe 82 is stable with time by 0.01 mag (Doi et al. 2010, arXiv:1002.3701). The response of each CCD and filter is also available.

Tables

Tables of camera sensitivity through each filter are available as html tables and as ASCII tables: u.dat g.dat r.dat i.dat z.dat

The columns of the table represent:

1. wavelength
2. on the sky sensitivity looking through 1.3 airmasses at APO for a point source. These define the survey's photometric system.
3. sensitivity under these conditions for very large sources (size greater than about 80 pixels) for which the infrared scattering is negligible (the infrared scattering only affects the thinned detectors used for ugri and among these, it is negligible for ug; hence this column is different from column 1 only for ri)
4. the response of the third column with no atmosphere
5. assumed atmospheric transparency at one airmass at Apache Point Observatory

Variation

The response functions of the SDSS imager as a function of wavelength have been monitored throughout the survey. The griz responses were stable over time, although very small seasonal (i.e., temperature) variations were observed, at a level well below our typical photometric errors. However, we have found a relatively large change in both the amplitude and shape of the u-band response, which is likely due to a degradation of the UV enhanced coating of the u-band CCD. This change in instrumental zero-point is effectively corrected by the photometric calibration for objects near the mean color of the standard stars, and, in fact, the repeat photometry of stars in stripe 82 is stable with time for stars with -0.5Arrangement of CCDs on the camera

*Text and figures on this page come from an author-created, un-copyedited version of the SDSS Data Release 7 paper, an article submitted to Astrophysical Journal Supplements. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. A preprint of the DR7 paper is available from the arXiv preprint server.